Archive for the ‘Volcanoes’ category

Big Pictures: Space Shuttle and Mount St. Helens

May 18, 2010

The Big Picture has been on a roll lately, with two sets of particular interest to planetary and space-types. First, is the feature on the final launch of the space shuttle Atlantis last week:

Second, today is the 30th anniversary of the explosive eruption of Mount St. Helens, and there are some amazing photos that show the devastating power of a volcanic eruption:

LPSC 2010 – Day 4: Mars Oceans, Titan Lakes, Astrobiology and Asteroids

March 6, 2010

Thursday started off with a couple of talks about the possibility of oceans on Mars. The first one, given by Gaetano DiAchille looked at possible locations of deltas all over Mars to try to figure out the water level of a past ocean. Deltas form when a river hits a standing body of water and drops its sediment, so they are a reliable marker of the water level. DiAchille found that “open deltas” – that is, deltas that do not end in a closed basin like a crater, all appear at the same elevation. This might mean that they all fed into a large northern ocean.

A map of valley network density on Mars and the possible extent of a northern ocean.

In the second talk, Wei Luo described his work mapping where all of the valley networks on Mars are and found that the northern limit of the networks fits with elevations that had previously been considered as possible ocean shorelines. The valley networks also matched with locations that atmospheric models predict would get the most precipitation.

Neither of these studies is conclusive evidence for a northern ocean on Mars, but they are interesting and they suggest that the “ocean hypothesis” is becoming popular again after years of little interest.

Later that day I saw a talk by Nick Warner describing the possible thermokarst lakes that he discovered in Ares Vallis on Mars. I wrote an article on Universe Today about this discovery when it was first announced a couple months ago.

I ducked out of the Mars talks to go see a talk by my friend Debra Hurwitz about a lava channel in a crater in Elysium Planitia. The channel was formed when lava breached the rim of the crater, flowed down the inner wall and ponded in the bottom. She calculated that the lava probably flowed at about 17-35 meters per second and that 6,000 cubic meters per second flowed down the channel for about 15 days. She also found that the channel could have been eroded mechanically without the need for the lava to actually melt the underlying rock very much.

A sketch of the lava channel filling the crater in Elysium Planitia.

After that, I headed over to the Titan session to hear a talk by Ralph Lorenz about waves on Titan lakes. Most of what we know about the surface of Titan, including the presence of liquid hydrocarbon lakes, is based on radar images from Cassini that measure roughness. The lakes show up as perfectly smooth (and therefore dark) surfaces, which is weird because radar images of lakes on earth usually have slight roughness due to waves. On Titan the gravity is lower, so you would expect bigger waves. It’s possible the lack of waves is due to the viscosity of the lakes, which might be increased by bigger “tar-like” molecules dissolved in the thinner ethane and methane, but it might also be due to a lack of wind. The Cassini mission will be watching as the seasons at Titan change to see if the wind changes and kicks up any waves.

A (suggestively colored) radar map of lakes on Titan.

I did a lot of session hopping on Thursday! The next stop was the astrobiology session. Oleg Abramov presented some results of his investigation of what intense impacts might have done to early life on the earth or Mars. He found that even during the Late Heavy Bombardment, the crust is not sterilized by the impacts, and in fact it might be more habitable for early life because impacts deliver organic molecules and cause widespread hydrothermal activity!

The talks I was really interested in were two talks on the magnetite crystals discovered in the famous ALH84001 meteorite. I posted a while back about a new paper that claims these crystals are evidence of life on Mars, and these two talks were focused on the claim. The first talk, by Allan Treiman gave some good background on the debate over whether ALH84001 preserves evidence of life and then addressed some of the new claims about the magnetite crystals. He said that most of the attributes of biological magnetite crystals, such as their size, lack of flaws, and precise crystal structure were not observed in the ALH84001 crystals. The big question is why the crystals are so pure. Allan argued that you can get pure crystals just from the heating of iron carbonate, which is found in the meteorite.

The following talk was by Kathy Thomas-Kleptra, whose paper Treiman was responding to. She showed that Treiman had probably made an error in calculating the breakdown temperature for iron carbonate. She also pointed out that the crystals are found in carbonates without much iron and that there is no graphite observed, but it is also a byproduct of heating the carbonates.

I don’t know enough about petrology and geochemistry to know who is right here, and I was very disappointed that both Kathy and Allan used up all of their time talking, so there was no chance at all for questions! I wasn’t the only one. When the moderator said that there was not time for questions and that they had to get on with the next session, most of the room groaned and protested. But alas, the talks pressed onward.

Biogenic magnetite crystals inside a bacterium one Earth.

I zipped back over to the Titan talks in time to catch the end of one pointing to features that they claimed were “deltas” in one of the lakes. I was very skeptical of this because the quality of the radar images is so low. What they avtuall observe is a dark branching channel that ends at a peninsula in one of the lakes. That’s not evidence for a delta in my book. This talk made me realize how spoiled I am with HiRISE, CTX, MOC and other high-resolution data on Mars!

Finally, I stopped by the asteroid session for two talks. The first was by Dan Scheeres and he talked about the role that tiny forces might play in holding asteroids together. He showed that Van Der Waals forces, normally ignored for all but the tiniest particles, actually might be important in holding particles together in asteroids. He made the analogy to powders like flour or cocoa powder on earth. These can clump together and when they are stressed the form fractures even though they are made of loos grains. The same thing might happen on a much bigger scale with the gravel and boulders in low-gravity asteroids!

It's possible that the fractures in objects like Phobos are more like the cracks you see in flour than like cracks in a solid, fractured rock.

The last talk I caught on Thursday was by my friend Seth Jacobson, who showed some simulations of asteroids that spin so fast they break apart. He showed that the ratio of sizes between the two bodies make a big difference in how the binary asteroid evolves. In some cases, the secondary asteroid even swings so close to the primary that it splats apart and forms a short-lived three-body system!

Model Mars Landscapes!

January 25, 2010

Check out these spectacular new photos of Mars! It certainly looks like the rovers have stumbled upon some more interesting terrain! The only catch is, these aren’t pictures of Mars at all, they are photographs of models made of, among other things, paprika, chili powder, and charcoal. They are the work of Matthew Albanese, and you need to go check out some of his other photographs. There are steel-wool tornadoes, faux-fur fields, and this spectacular glowing volcano:

(Hat tip to Ann Martin, fellow Cornell Astronomer and blogger at the ALFALFA blog for sharing the link to these pictures!)

Lava Tubes on the Moon!

November 25, 2009

Image credit: JAXA/SELENE

Ever wonder how astronauts on the moon are going to avoid deadly space radiation? One option is to live in caves, and luckily the Kaguya team has found one! Read more about it in my article over at Universe Today.

Volcanic Explosion Seen From Space

July 1, 2009

This is completely awesome:

(Courtesy of Ian O’Neil and Richard Drumm)

Olympus Mons is How Tall?!

May 23, 2009

Olympus Mons is a big volcano. It is almost unimaginably huge. It is 550 kilometers (342 miles) across at its base, and the volcanic crater (the technical term is ‘caldera’) at the peak is 80 kilometers (53 miles) long. If you were standing at the edge of the caldera, the volcano is so broad and the slopes are so gradual that the base of the volcano would be beyond the horizon. That’s right, it is a volcano so big that it curves with the surface of the planet.

And it is tall. 27 kilometers tall. That’s 16.7 miles from base to summit. 88,600 feet. That’s about three times as tall as Mt. Everest. Even Mauna Kea, Earth’s own giant shield volcano doesn’t come close. Measured from the sea floor to its summit, Mauna Kea is 33,476 feet (10.2 km) tall: taller than Everest, but only about 40% the height of Olympus Mons.

The state of Hawaii, compered with Olympus Mons.

The state of Hawaii, compared with Olympus Mons.

Ok, so throwing those numbers around is fun if you like stats, but it still doesn’t convey quite how tall Olympus Mons is. So here’s an eye opener. Olympus Mons is so tall that it essentially sticks up out of Mars’s atmosphere. The atmosphere on Mars is thin to begin with, but at the summit of Olympus Mons, it is only 8% of the normal martian atmospheric pressure. That is equivalent to 0.047% of Earth’s pressure at sea level. It’s not quite sticking up into space, but it’s pretty darn close. In fact, it was first confirmed to be a huge mountain when Mariner 9 saw it towering above the top of a global dust storm like an island in a rust-colored sea.

Mariner 9 photograph of Olympus Mons towering above the clouds on Mars.

An airbrush painting of Olympus Mons towering above the clouds by Gorden Legg, a Hollywood artist, based on Viking Orbiter mosaic P17444.

Finally, since it is fun to compare Olympus Mons to Mauna Kea, what would the pressure be like at the summit if we placed Olympus Mons next to Mauna Kea in the Pacific? In that case, the summit of Olympus would be 21 km (68,897 ft) above sea level: still higher than Everest, and about twice as high as normal jets fly. The atmospheric pressure at the summit would be about 4.6% that at sea level. For comparison, at the top of Everest it is about one third the pressure at sea level, and most people still need to use oxygen canisters.

Olympus Mons is huge. Hopefully these numbers give you a little better idea of just how huge. If you’re wondering how it got to be so big, I already wrote about that in this post about shield volcanoes, so go check it out!

The tallest mountains on Mars, Earth, and Venus compared. Note that the horizontal scale is drastically squashed.

The tallest mountains on Mars, Earth, and Venus compared. Note that the horizontal scale is drastically squashed.

Big Pictures of Mount Redoubt Eruption

April 6, 2009

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The Big Picture, an awesome photo-blog that you should be reading, has a very cool set of photos of the Mount Redoubt eruptions in Alaska. I thought it was especially cool to see how the glacier on top of the mountain is collapsing as it melts from beneath.

Update: Just like last time the Big Picture posted volcano photos, global warming deniers are posting in the comments and claiming that volcanoes make much more CO2 than humans, and therefore global warming is not man-made. Luckily, another commenter (#37) posted a very well-researched response on the Big Picture site. The Hawaii Volcano Observatory has also addressed this question: “Which Produces More CO2, Volcanic or Human Activity?”

The answer: on average, volcanoes produce less than 1% as much CO2 as fossil fuels do.

The Painted Desert and Petrified Forest

March 22, 2009
The colorful layers of the painted desert formed in the triassic period when meandering tropical rivers deposted layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.

The colorful layers of the painted desert formed in the triassic period when meandering tropical rivers deposted layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.

(This is the final day of a week-long field trip in Arizona. Get caught up with days 1,2,3,4,5, 6)

Friday was the last day of the field trip, and we spent it at the Petrified Forest national park. We were there to study the colorful clays and river deposits, but we began the day with an unexpected bonus: our guide, Bill Parker, is a paleontologist at the park, and he took us to see some of the skeletons that have been found there, and the people who work on them. I spent much of my childhood wanting to be a paleontologist, so to actually see it in action was a special treat. We learned that there is recent evidence that almost all dinosaurs had feathers! We also got to see the reconstruction of what one of the animals may have looked like based on the skull, which was something that I didn’t realize that paleontologists did.

A paleontologist at Petrified Forest national park chips away at the protective plaster around the skull of an alligator-like dinosaur.

Matt Brown, a fossil preparer at Petrified Forest national park chips away at the protective plaster around the skull of an alligator-like dinosaur.

A reconstruction of what one of the dinosaurs may have looked like, based on its skull.

A reconstruction of what one of the dinosaurs being studied at the park may have looked like, based on its skull.

After the paleontology lab, we continued on to the painted desert badlands, which were the real reason we came to the park. These beautiful formations were formed when Arizona was a flat, tropical floodplain. Many of the layers are actually the deposits from broad, meandering rivers. When they overflow their banks, they deposit sediment in broad layers. In other cases, ash from volcanic eruptions blanketed the landscape, and was altered by the water of the lakes and rivers and rain to become clay minerals like bentonite. The clays expand when they get wet and contract when they dry, and are quite soft to begin with, so that it is very difficult for plants to get a foot-hold. This leads to broad expanses of “badlands” terrain: heavily eroded buttes and mounds of the brightly colored clays and sandstones.

The badlands terrain of the painted desert. The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.

The badlands terrain of the painted desert. The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.

We spent a long time studying an outcrop that used to be part of an ancient meandering river or delta. The layers deposited on the shore of a river tend to be angled in toward the riverbed, so by looking at the orientation of thelayers, you can guess at what the river might have looked like.

img_1537_smallClay-bearing river or delta deposits. These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!

Clay-bearing river or delta deposits. These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!

We were especially interested in this outcrop because we found fossils of giant horsetail plants in them, and the fossils were upright, as if they had been covered in sediment while still alive. That would mean that something like 8 feet of rock was deposited extremely rapidly, before the horsetail died and fell over! We speculated that this could happen during a particularly heavy monsoon season. In the layers with the horsetail there were also some very large rocks that were rounded as if they had been transported by the river.

One of our paleontologist guides, pointing at the two giant horsetail fossils. (click for full-resolution to see the fossils more clearly)

Jeff Martz, one of our paleontologist guides, pointing at the two giant horsetail fossils. Click for full-resolution to see the fossils more clearly.

A close-up of one of the horsetail fossils. The green part is a couple of inches across.

A close-up of one of the horsetail fossils. The green part is a couple of inches across.

After puzzling over the river deposits and trying to reconstruct their story, we ended the visit to the park by taking a look at the petrified forest. Our guide, Bill Parker, told us that all of the petrified trees in the park are missing their bark and branches, and that they likely were part of log jams in ancient Triassic rivers. He pointed out that it is almost impossible to find a modern river that hasn’t been modified by humans, and that in their natural state, these meandering rivers would have been clogged with dead trees. When the trees were buried by sand and ash, the silica in the rocks was dissolved in the water and precipitated out in the cells of the wood, gradually replacing organic matter with silica. The silica logs are much more resistant to erosion than the sandstone in which they are embedded, so as the rock erodes away, the logs are left sitting on the surface.

Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.

Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.

You may be wondering what all of this has to do with Mars. Well, the paleontology has very little to do, but the processes involved are quite relevant. Mars likely had liquid water in its past, and certainly had ash and sand deposits. Places like Mawrth Vallis have clay-bearing rocks eroded into channels and buttes and mounds, very similar to the clay-bearing rocks of the painted desert. The same conditions that prevailed to preserve the petrified forest and the dinosaur and plant fossils may also preserve more basic biomarkers, capturing evidence for a habitable Mars.

That concludes our geologic tour of Arizona! I went the first version of this trip two years ago, and then as now I was humbled by how complex and difficult to interpret our planet is, even when we can reach out and touch the rocks and analyze them at our leisure. On the other hand, there were many things that we saw from the ground that were much easier to interpret from aerial and satellite data. When you’re on the ground, it is much harder to get an feeling for the overall shape of what you are looking at. A combination of both orbital and ground-based studies is very important to really begin to understand the geology in detail, and even then there is a lot that we can’t figure out!

This trip has also impressed upon me how much more geology I need to learn. I need to know sedimentology and stratigraphy if I’m going to be attempting to read the story hidden in the layered pages of rock on Mars. But for now, I at least know what it is that I don’t know, and that’s a good start.

Grand Falls and Sand Dunes

March 20, 2009
An aerial view of Grand Falls and the dune field that we visited. Grand Falls is indicated by the marker. You can clearly see where lava blocked the previous course of the river.

An aerial view of Grand Falls and the dune field that we visited. Grand Falls is indicated by the marker. You can clearly see where lava blocked the previous course of the river.

(This is day 6 of a week-long field trip in Arizona. Get caught up with days 1,2,3,4,5)

Today we visited Grand Falls and the nearby dune field. Grand Falls is especially interesting because it combines many of the processes that are active in shaping planetary surfaces. The falls are the result of a huge lava flow pouring into the ancient canyon of the Little Colorado river, filling the canyon and flowing both up and downstream for many miles. Obviously this had quite an impact on the river! It formed a dam and a lake upstream until finally the lake spilled over the top of the lava dam and began carving a new course for the river. Basalts and other lava rocks are very hard compared to the Kaibab limestone and Moenkopi siltstones of the original canyon, so the huge tongue of lava is preserved, byt the river is currently working on carving a path around it in the softer rocks. The result is Grand Falls:

On the left you can see the dark, erosion resistant basalt that dammed the original canyon. On the right, Grand Falls are busy carving a new course for the river into the softer rock around the obstruction.

On the left you can see the dark, erosion resistant basalt that dammed the original canyon. On the right, Grand Falls are busy carving a new course for the river into the softer rock around the obstruction.

A mosaic of Grand Falls. Huge blocks of limestone sit at the bottom of the falls, showing that they are a powerful erosive force. (Click for full-resolution)

A mosaic of Grand Falls. Huge blocks of limestone sit at the bottom of the falls, showing that the falls are a powerful erosive force. (Click for full-resolution)

The other main point of interest at Grand Falls were the interesting patterns of cracks in the massive lava rock. These cracks, of “joints” tend to form perpendicular to surfaces in the flow that have the same temperature. In very simple flows, the joins often are vertical and the rock looks like it is made out of hexagonal columns. At Grand falls, the joints are mostly very jumbled, which probably means that steam was percolating through the rock as it cooled. This might mean that there was water in the river when the canyon was filled with lava (the Little Colorado doesn’t always have running water in it).

Columnar joints in the basalt flow at Grand Falls. This is one of the more ordered sets of joints; in many places there is no clear texture to the rock, suggesting complicated interactions with water as the lava cooled. Note that the normally-black basalt is stained tan-colored by the silt-bearing mist from the falls, yet more evidence that they are constantly eroding the rock that they flow over.

Columnar joints in the basalt flow at Grand Falls. This is one of the more ordered sets of joints; in many places there is no clear texture to the rock, suggesting complicated interactions with water as the lava cooled. Note that the normally-black basalt is stained tan-colored by the silt-bearing mist from the falls, yet more evidence that they are constantly eroding the rock that they flow over.

After Grand Falls, we drove our rental minivans through a shallow part of the river upstream, over some very rough roads, and arrived at a nearby dune field. This field is quite young: in the 1930s there were no dunes, but by the 1950s there were, and now no new dunes seem to be forming. The source of the sand is the bed of the Little Colorado, but there are also lots of dark volcanic cinders in the dunes. Larger gravel-sized particles get pushed around by small sand sized particles and form “granule ripples”. These are extremely common on Mars; the Opportunity rover is currently in the middle of an expansive plain of similar ripples.

Granule ripples. The larger, more dense basalt granules end up at the crest of the ripple, where finer-grained sand is blown away or settles below the granules. (in the background are the San Francisco Peaks, an extict stratovolcano)

Granule ripples. The larger, more dense basalt granules end up at the crest of the ripple, where finer-grained sand is blown away or settles below the granules. (in the background are the San Francisco Peaks and a few much smaller cinder cones)

Larger piles of sand form dunes. Dunes move as the wind blows sand up their slope and deposits it at the top until it becomes too steep and avalanches down the “slip face”. Here is an example of a boomerang-shaped “barchan dune” with a nice slip-face. This type of dune is very common on Mars.

A boomerang-shaped "barchan dune". The points, or "horns" of the dune point in the direction that the wind is blowing. In this image, the wind that formed the dune was blowing roughly from right to left.

A boomerang-shaped "barchan dune". The points, or "horns" of the dune point in the direction that the wind is blowing. In this image, the wind that formed the dune was blowing roughly from right to left.

That’s all for today. Tomorrow we will be visiting the painted desert, a location that may be similar to Mawrth Vallis on Mars, one of the potential MSL landing sites.

Meteor Crater, Walnut Canyon, and Red Mountain

March 19, 2009
Meteor Crater is the best preserved (and the first recognized) impact crater on Earth.

Meteor Crater is the best preserved (and the first recognized) impact crater on Earth.

(This is day 5 of a week-long planetary geology field trip to Arizona. Get caught up with days 1,2,3,4)

Today was a long and awesome day. We started out at meteor crater, the youngest and best preserved impact crater on Earth! Our guide today was Shaun Wright, a colleague from the Hawaii field workshop, among other places. He showed us infrared images of the crater taken from an airplane and we walked around the rim trying to identify the main compositions detected. Meteor crater is especially nice for this because it excavated into three distinct layers: the red Moenkopi siltstone (the surface of the surrounding plains), the yellowish Kaibab limestone (normally beneath the Moenkopi), and the white Coconino sandstone (below the Kaibab).

Back in the early 1900s, people were trying to dig and find the iron meteorite that they thought was buried under the crater. (it turns out the meteorite was blasted into thousands of pieces upon impact) Luckily, the mining work carved a notch in the rim that lets you see the three units of the crater where they have been overturned by the impact. When a large impact occurs, it lifts up the ground and forms an “overturned flap” at the rim. You can see in the picture that the Moenkopi goes from relatively solid-looking to very fractured-looking, and is then overlain by blocks of Kaibab and Coconino.

At the rim of the crater, the impact has reversed the sequence of layers. The red Moenkopi would normally be on top but here it is overlain by blocks of Kaibab limestone and Coconino sandstone that have been excavated by the impact.

At the rim of the crater, the impact has reversed the sequence of layers. The red Moenkopi would normally be on top but here it is overlain by blocks of Kaibab limestone and Coconino sandstone that have been excavated by the impact.

Another very interesting part of the crater is that the impact pulverized the coconino sandstone, crushing the sand grans into powder. This powder was actually mined for a while because it is a very high grade silica “rock flour” used in things like makeup. Amazingly enough, even though it has been subjected to one of the most violent forces imagineable, the crushed sandstone still maintains its original structure, and you can even see crossbeds preserved!

The shocked sandstone still preserved very fine cross-bedded layers, but can be crumbled into a power with your hand.

The shocked sandstone still preserved very fine cross-bedded layers, but can be crumbled into a power with your hand.

After Meteor Crater, we made a short stop at Walnut Canyon, where the Coconino sandstone is not shocked and the crossbeds are displayed prominently. Remember, cross-bedded layers typically form when sand dunes are lithified in place and turned into sand stone, preserving the layers within the dune. ForĀ  more info about crossbeds, check the USGS site about them.

Crossbeds at Walnut canyon are essentially fossilized sand dunes from when Arizona was a coastal desert. The direction that the layers are tilted tells us that the prevailing winds blew from north to south.

Crossbeds at Walnut canyon are essentially fossilized sand dunes from when Arizona was a coastal desert. The direction that the layers are tilted tells us that the prevailing winds blew from north to south, although the various sets of layers in this image actually reflect several wind directions.

Finally, after Walnut canyon we drove up to Red mountain, which is a cinder cone volcanoe that has been carved open by erosion. Not only does it give a great view of the interior structure of the cone, it also erodes into a very bizarre landscape that looks like it belongs in a Dr. Seuss book.

The interior of Red mountain cinder cone. The layers are from different stages of the eruption that deposited cinders with slightly different composition or weathering properites. The bizarre shapes are due entirely to erosion, mostly by water.

The interior of Red mountain cinder cone. The layers are from different stages of the eruption that deposited cinders with slightly different composition or weathering properites. The bizarre shapes are due entirely to erosion, mostly by water.

That’s all for today. Tomorrow we are off to Grand Falls and the nearby dune field!